Call Numbers - How Do They Work?

 Books are shelved alphabetically, based on the first letter of the top line of their call number.

So, if I were looking for a book with the call number RC113.5 .R33 2010 I would walk down the alphabet until I found the R's. Then, once I've found the correct letter, any call number that starts with ONLY that letter - in this case, any call number starting with JUST R - would be at the beginning.

Then the R's are followed by the RA's, RB's, RC's and so on through the RZ's. Even after you've found the correct section of letters, especially if you're browsing in a library that has a lot of books you may find that there are rows of books whose call number begins with RC. All call numbers that start with the same letters will then be in order numerically by the number directly after or under those letters. In the picture below you see 4 books with RA call numbers, but note they are in numerical order based on that second line.

Most of the time, it will be easy to find the book you're looking for by this point. But, if you do encounter many books with the same letters and numbers, you may need to use the next line. In the picture below, note that there are 2 RC113.5 books, but they are in alphabetical order by that third line, R before S.

If you think you've got the hang of it, try playing the game "Within Range" by Carnegie Mellon University: https://libwebspace.library.cmu.edu/libraries-and-collections/Libraries/etc/ After you click, go to the link called "Within Range." Once in the game, click on a book from the stack on the left side of the screen and try to place it correctly on the shelf. Although this game is just for fun, playing it can help your understanding of call numbers immensely!